Passive magnetic components, such as coils or transformers, are required for a large number of applications. For example, at the moment, up to 300 passive components are processed in a mobile radio telephone, with major functions being carried out by magnetic components. Every extension in function, irrespective of whether this is a dual band or dual mode extension, increases the number further. The mounting, the soldering and the testing of the individual components, which are becoming ever smaller, in this case are the cause of a major proportion of the costs for the equipment manufacturers. In this case, coils and inductors have frequently been produced until now using a thick film technique on ceramic substrates or as air-cored windings. Although these coils have high Q-factors, they are relatively expensive. In this case, the Q-factor Q of a coil is calculated from the ratio of its inductance L to its resistance R. In this case, Q=ωL/R where ω−=2πf and the value of Q is normally determined at a frequency f=1 GHz.
In order to reduce the production costs, the aim of many developments is to integrate a large number of passive components, such as filters, passive networks, RF inductors, and, in particular, magnetic components on one chip. Integrated inductors are at the moment virtually exclusively in the form of planar spiral coils, which are normally arranged on the uppermost metalization plane. As a rule, the coils are composed of metal (for example Al, AlSiCu, Cu) so that they have a relatively low electrical resistance. In consequence, it is possible to produce integrated inductors which achieve a Q-factor of up to about 15 at a frequency of 1 GHz. Spiral coils such as these are described, for example, in the documents J. A. Power et al., “An Investigation of On Chip Spiral Inductor on 0.6 μm BiCMOS Technology for Application”, 1999 IEEE Int. Conf. on Microelectronic Test Structures, Vol. 12, Ireland 1999 pages 18-23 and A. Gromov et al., “A Model of Impedance of Planar RF Inductors Based on Magnetic Films,” IEEE Transactions On Magnetics, Vol. 34, No. 4, Jul. 1998, pages 1246-48.
Unfortunately, spiral coils such as these also have a large number of disadvantages which have until now prevented higher Q-factors from being achieved. A spiral coil is based on conductor rings which, as the number of turns increases, carry the conductor in the interior of the surface which is surrounded by the first ring. The jointly surrounded flux area A of all the turns and the flux concatenation which is associated with it are thus increasingly reduced in magnitude. In order to compensate for this, the overall extent of the spiral coil must be correspondingly enlarged, so that additional chip area is required.
Furthermore, the magnetic flux element which flows through the electrical conductors causes eddy currents in the conductor material, which in turn results in additional losses.
However, the main problem of planar spiral coils is in the direction of the magnetic flux since, due to the alignment of the spiral coils, the majority of this magnetic flux is necessarily carried through the substrate. Parasitic eddy current effects likewise occur there, depending on the substrate conductance, and their resistive losses decrease the coil Q-factor. The described effects mean that integrated spiral coils on conductive substrates (p<20 Ωcm) have only relatively low Q-factors (Q<15). Despite major efforts by the component manufacturers, it has until now not been possible to develop integrated spiral coils with a Q-factor of more than 15 for large-scale production.
The use of ferromagnetic materials with high permeabilities has therefore been proposed in order to increase the Q-factor of inductors. Thus, for example, the document M. Yamaguchi et al., “Characteristics and Analysis of Thin Film Inductor with Closed Magnetic Circuit Structure” IEEE Transactions On Magnetics, Vol. 28, No. 5, Tohoku University in Japan, Sep. 1992, pages 3015-17 discloses experiments with Permalloy for embedding planar coil conductors. The planar coils were integrated on a glass substrate between two Permalloy layers. Similar coil concepts are also disclosed in the document T. Inoue et al., “The Effect of Magnetic Film Structure on the Inductance of a Planar Inductor,” IEEE Transactions On Magnetics, Vol. 34, No. 4, Japan, Jul. 1998, pages 1372-74 and JP 06-084639.
Since the magnetic field H is at right angles to the magnetic layer in all these coil concepts, the way in which the magnetic flux is carried is, however, highly ineffective. Furthermore, a closed magnetic flux can be achieved, by virtue of the technology, only with great difficulty, and air gaps between the layers decrease the effective permeability of the flux circuit.
In order to make it possible to use the characteristics of ferromagnetic materials more effectively, the use of helical coils (solenoids) or annular coils (toroids) with ferromagnetic cores has also been proposed. Integrated inductors such as these have been disclosed, for example, in the documents EP 0 725 407, U.S. Pat. Nos. 5,279,988, 5,998,048 and 6,008,102 and the diploma thesis by Ulrich van Knobloch, “Herstellung und Charakterisierung von integrierten Hochfrequenzspulen mit magnetischem Kern” [Production and characterization of integrated radio-frequency coils with a magnetic core], Institute for Semiconductor Technology and Materials for Electrical Engineering at the University of Hanover.
In this case, unfortunately, it has been found that although the proposed helical coils with ferromagnetic cores make it possible to increase the Q-factors of the coils, the increase in the Q-factor is, however, generally not sufficient to justify the likewise increased production cost for manufacturing the ferromagnetic cores. The present invention is therefore based on the object of providing a magnetic component whose parameters are considerably better than those of the previous magnetic components, in particular with a considerably better Q-factor.